The requirements of relative physical position and timed interrelated movement between cooperating stitch forming instrumentalities of a sewing machine are extremely critical. In conventional sewing machine construction utilizing an external frame in which the parts are assembled, the need for such critical relationships causes the imposition of severe limitation on the frame design to insure requisite rigidity and stability and requires costly and time consumming frame forming and machining operations for requisite tolerance control between the operative stitch forming instrumentalities.
In known skeletal frame sewing machine constructions, such as disclosed in U.S. Pat. Nos. 2,741,202, Apr. 10, 1956; 2,793,600, May 28, 1957; 2,946,302, July 26, 1950 and 3,420,200, Feb. 3, 1966, the external casing, when utilized, serves primarily as decorative cover with perhaps support for controls, illumination, indicia, and the like with result that the costly and time consumming manufacturing requirements are not reduced but rather are simply transferred from the external to the skeletal frame.